EP-0 080 446 (Atlas Copco AB) discloses a rock drilling machine, wherein the feeding force is transmitted from the housing to the drill string or the drill string adapter over a damper. The damper yields from the reflected compressive shock waves and the yield is detected and used to control a control pin which adjust the stroke length for the percussive piston such that the reflective shock wave energy is minimized.
In particular, the control pin is an adjustment means which adjusts in what axial position of the percussive piston a pressure signal is transmitted to a to-and-fro moveable valve body, wherein means are arranged in order to control the control pin as a response to the pressure signal such that the operation of the percussion device is modified for reduction of reflected shock wave. In an alternative embodiment the control pin is controlled after analysis of a drilling parameter in connection to the drill string.
The known drilling machine functions well but is gives limited possibilities to easily control the axial turning-positions of the percussive piston.